Update src/solutions/1_einstein_model.md, mkdocs.yml files

mkdocs.yml

@@ -31,6 +31,8 @@ nav:
     - Magnetism: 'lecture_8.md'
     - Fermi surface periodic table: 'fermi_surfaces.md'
     - Extra exercises: 'extra_exercises.md'
+  - Solutions:
+    - Lecture 1: 'solutions/1_einstein_model.md'
 
 theme:
   name: material

src/solutions/1_einstein_model.md

+# Solutions for lecture 1 exercises